|Installation of JBM Industries replacement diaphragms on Keihin CV carburetors used on vintage motorcycles such as
the Honda V4 engined bikes like VFR400R, VFR400RR, V-65 Magna, and also NC-30 , VTR250, PC800. These
vintage Honda motorcycles have a problem with old diaphragms that shrink from ethanol fuel and age. Some are
destroyed by carburetor cleaners sprayed down the wrong hole while the diaphragm or membrane is still on the
Installation of these replacement diaphragms is not difficult, but should only be done by someone with mechanical
skills. This diaphragm was replaced in 15 minutes including the time it took to make these photos. This diaphragm is
used on other makes of vintage motorcycle, including the Honda 1100 V4 engine, CB1300, X4, etc. Please see our
"HOW TO MEASURE" page. The Keihin VG series page may also be helpful to you, so please check it out.
This page shows installation of JBM part K-72-S , a 72 mm diameter diaphragm or librane with key. This
shows mounting the central tire on a plastic CV carb slide or piston. JBM Industries uses TSR compound.
|USE SMALL, SHARP, SIDE CUTTERS, or JEWLERS SAW. SLIDES ARE BRITTLE
|It is important that you take your time on installation. Do not rush.
See other instructions for more ideas on this site.
See testimonials from others listed on this site.
|Roll the diaphragm when you install it so it
looks like the photo above.
|1983 Honda Shadow VT750
I used a set of these diaphragms and they are Great. When installed they are slightly thicker which made it just a touch stiff. After I got the bike cranked, it ran
great. Thanks for producing something that Honda quit producing.
I received your products earlier today for Honda V-65 Magna, and I can't believe how fast they got here! The diaphragms are amazing. I have decided to replace
the other two so please ship two (2) more K-72-S diaphragms to me. I will look for your invoice in Pay Pal. I plan to pass your info along to some of the other retro
bike dealers and garages in the area. Hope you can benefit. Thanks for everything. ....Brian Tucker
I just wanted to say thank you. Those K-72-S diaphragms you sold me fit my 2001 Honda shadow spirit like a glove. Appreciate you getting them mailed out as
quickly as you did. I will definitely tell all my friends about your products.
Hi Don: Date: Tuesday, February 26, 2013, 2:06 PM
I just wanted to give you a brief update. I was finally able to install and test your slide diaphragms. The installation went well. I used a 5-minute epoxy rather than
Super Glue. That seems to hold very well (maybe too well if I ever needed to replace these). The only bothersome part was some of the slide tops broke off more
than I would like when removing the top ring. It looks ugly, but works fine.
We have only run the diaphragms for a few dyno pulls compared to our other carbs, but your slides seem to react better, snappier, and during a slide-speed test,
yours respond BETTER than ours :-) The bike makes the same, or better horsepower and doesn't seem to have any hesitation or slowing in pull. These were all
my concerns, that are now gone.
I was also able to ride the bike for one session at the track. It felt fantastic! But, it's a much faster bike than I am used to, so I also didn't ride it hard. However, that
was an even better test for the diaphragms since I was always at partial throttle in the turns. Throttle modulation was never off or odd.
I will probably be ordering a bunch more here in the next few weeks. Are you limited in supply? I see the need for 12 diaphragms right off the top of my head.
There maybe another 12 to 16 diaphragms needed after a quick e-mail to the group. If you need to make them, what is your turn-around time?
Thank you again for your help with this. We are very excited to have found a solution to a problem that has plagued us for a very long time.
G-Force Engine Development
www.mngforce.com There is no such thing as "Too Fast"
Looks to me like you used our K-72-S, and I checked stock. I can sell you 12 of them without any problem or delay. I am glad they worked out for you.
Our TSR compound is made without much stretch, but it does not use fabric to limit the stretch. If the rubber stretches, it is just lost motion. If the rubber stretches,
it will eventually stay stretched and the diaphragm will look rounded and have a lot of "slack" it it. Sometimes the ethanol in the fuel causes this over time. ( Some
folks call it a case of the "baggies".)
There is a page on the JBM site that shows how to repair broken plastic slides with a metal bushing. You do need to be real careful on plastic slides as
some of them are very brittle.
Good Luck with your project and thanks for your report, Don @ JBM
Hi mate my name is Lawrence borg I recently brought some diaphragms of u and they are brilliant. Better then the original by far. I would also like an invoice for
another 6 Keihin K'72,S diaphragms for My Honda VF 1000 F2 Its a 1985 model please. Laurie. Australia thanks mate.
Keihin K-72-S Diaphragm: Smaller hole for METAL SLIDES Fits Keihin carbs used on 88-89 Honda NT650 Hawk GT (RC31) also CB1300 & X4
Note: You can add the HONDA '89 PC 800 to the list for the K-72-S. They fit like a glove. Thanks, Peter Hassing
|JBM Industries diaphragm performance information on our K-72-S membranes installed on plastic throttle slides:
|(K-72-S) diaphragms: I installed these diaphragms on 3 Hitachi HSC34
Carburetors. These were standard issue carburetors on Yamaha XS850
motorcycles from 1980 and 1981. The groove diameter on the Carb itself is
actually 73mm, but the dish and slide groove measurements are the same. Also,
the key is slightly smaller on the Hitachi than it is on the Keihin. With a little
trimming of the key, I was able to install them with little issue, and they work Great.
In case anyone asks in the future, These are a great fit for the XS850 / 3 cylinder
with Hitachi Carbs. From: "Brian Webster" email@example.com